This invention relates to a needle bearing and also to a speed reducer using this needle bearing.
One known conventional needle bearing is disclosed, for example, in the above JP-UM-A-52-124353. This bearing comprises a retainer of an annular shape which includes a cylindrical tubular portion having a multiple of rectangular restriction holes (which are formed therein, extend in an axial direction, and are spaced at equal intervals in a circumferential direction), and also has flange portions projecting radially inwardly respectively from opposite axial ends of the cylindrical tubular portion, and a multiple of needle rollers which are received at their radially-outward end portions in the restriction holes, respectively, and are restricted in axial movement by the flange portions. A radial length of each of the flange portions is slightly smaller than the diameter of the needle rollers.
Such a needle bearing is provided between a shaft (internal member) and an external gear (external member) of a speed reducer (for example, an eccentric rotary-type speed reducer) as disclosed in JP-A-8-226498, and when the internal and external members are rotated relative to each other, an inner ring of a conical bearing, provided between the shaft and a carrier, can be brought into sliding contact with the flange portion of the retainer of the needle bearing, thereby limiting the axial movement of the whole of the needle bearing.
In the above needle bearing, there are occasions when the needle roller is skewed relative to its normal rotation axis because of misalignment. In such a case, this needle roller imparts a large axial force (skewing force) to the retainer. However, the retainer must have enough rigidity to withstand such an axial force, and therefore there were encountered problems that the material for forming the retainer was limited to steel and that a wall thickness of the retainer need to be larger than a predetermined value.